Recent Highlights on Solid Oxide Cells, Stacks and Modules Developments at CEA

Solid Oxide Cell (SOC) technology is a versatile technology able to operate either in electrolysis mode (SOEL), to produce hydrogen at high efficiency, in fuel cell mode (SOFC) using different fuels (carbon-based or non-carbon based like ammonia), in reversible mode (rSOC) with different cycles between electrolysis and fuel cell modes depending on the use case and the type of upstream coupling with renewable energies, and finally in co-electrolysis mode (co-SOEL) to produce syngas out of steam and CO2. Though proofs-of concept have been achieved at different relevant scales for those different operating modes, some R&D works still need to be performed to improve performance, durability and cost in a concomitant way, to meet the targeted key performance indicators as set by the EU for instance. Improved and upscaled cells and stacks need to be developed, with a methodology combining multiscale and multiphysics modelling, electrochemical characterization in relevant conditions and post-test analysis. Their integration into modules made of several stacks is also a stepping stone in order to reach multi-MW electrolysers as needed to meet the targets set by the RePowerEU plan intending to install 100 GW of electrolysers in EU in 2030 [1]. CEA is working on the whole value chain of SOC technologies, from cell development and optimisation to module design and operation through stack upscaling. Regarding SOC cells, the process has been optimised to obtain a good reproducibility on the cell performances (figure 1a). A current density of – 0.8 A/cm² has been reached at the thermoneutral voltage at 700°C. Works are in progress on the electrodes microstructures and interfaces to further increase the performances. After validation at single cell level, 100 cm² and 200 cm² cells active area have been produced with a good reproducibility and validated at short stack level. As far as stack developments are concerned, CEA continued its program on upscaling [2]. In parallel, improved seals are developed to increase the stack robustness to transient operation and interconnect coatings are developed using different deposition techniques. Those components have been first validated at sample scale before integrating them into short stacks and full-stacks for validation in real configuration. For instance, the integration of interconnect protective coatings in short stacks has been evaluated over more than 4500h of operation. Finally, a 4-stack module has been developed and put